Detachable drill bit



Patented Oct. 25, 1932 PATENT OFFICE CHARLES W. DE WITT, OF OAKLAND, CALIFORNIA.

DETACHABLE DRILL BIT Application filed July 31,

This invention relates to improvements in drill bits, and it consists of the constructions, combinations and arrangements herein described and claimed. 5 An object of the invention is to provide a drill bit especially adapted for use in mining, although not confined to such use, an outstanding purpose being to provide a detachable bit which is so`constructed that when 13 applied to the shank will have the blow delivered approximately medially of its mass.

Another object of the invention is to pro-` vide a detachable drill bit in` which the confronting end of the shank with which it is connectable is peened or made convex to match a corresponding portion of the bit for the purpose of preventing the successive blows on the shank from spreading said confronting end out and thus making the removal of the bit ditiicult.

A further object of the invention is to provide a detachable drill bit tempered on a graduated order so that the zone of extreme hardness is confined to the cutting faces and a zone of more moderate hardness is contined to the rim, the latter being for the purpose of preventing the wings of certain interlocking means from breaking out.

Other objects and advantages will appear in the follojving specification, reference being had to the accompanying drawing, in which Figure 1 is a side elevation of the improved drill, and

Figure 2 is a partially elevational and sectional View of the drill, the bit being in the unlocked position.-

This invention is an improvement on the detachable drill bit for which application for Letters Patent was filed'by Charles W. De Witt, July 2, 1928, Serial No. 289,848. So much of the instant drill which has structure in common with that of the foregoing application is briefly described as follows:

The shank 1, which is customarily made of steel, terminates at one extremity in a cylindrical plug 2. This plug fits in the recess 3 of the bit 4 which, according to the principle of the invention, is made detachable.

For the latter purpose the plug 2 has a pair of lugs 5 which coact with wings 6 in 1930. sen'ai No. 472,105.

the recess 3 in order to establish an interlock between the two parts. In order that a Slight turn of one part in reference to the other, for example, the shank 1 in reference to the bit 4, may efl'ect a tight connection, the upper 55 and lower edges of the respective lugs 5 and wings 6 are beveled as at 7 and 8. It is readily understood that a slight turn of the shank 1 following the insertion of the plug 2 in the recess 3 will make an absolutely tight connection between the two parts that will endure as long as the tool remains in effective use.

The improvements comprise the following: The plug 2 is generally longer than the recess 3. This spaces the shoulder 9 of the shank 1 from the upper edge or rim 10 of the bit 4 as at 11. The extremity of the plug 2 bears on the floor of the recess 3, and since the floor of the recess is located approximately 70. medially of the bit 4 it follows that the blows s delivered to the shank 1 will be transmitted to the middle region of the bit 4 and Will not be delivered to the rim 10.

There are a number of advantages in this particular feature of the construction. The bit 4 is maintained in better balance by virtue of the blows being delivered medially thereof. If the shoulder 9 and rim 10 were in contact there would be a division of the blow, a part of the force being delivered to the floor of the recess 3 while the remainder would be delivered to the rim 10. In addition to the disadvantage of this division of the force there is the ever-present possibility of fragments of the rim 10 being broken away. This is undesirable because it will work the ultimate destruction of the bit 4 but an adequate remedy for the condition is aforded by spacing the shoulder 9 as indicated.

That portion of the plug 2 contacting the bit 4 is rounded or peened at 12. The convexity thus provided is matched by concavity 13 in the floor of the recess. The annular portion of the plug 2 occurring where the peen 12 meets the sides of the cylindrical plug 2 is chamfered at 14. The purpose of this chamfer is to insure the offsetting of the edge of the plug 2 from the floor of the recess 3, 10

and an equally important purpose is to keep the lugs clear of the floor.

It therefore follows that the full force of I each blow is concentrated in the concavity 18,

the efl'ect of which is to work a restriction on the peened end 12, prevent-ing the latter from spreading. Should there be any evidence of spreading of the peened end 12 under extraordinary circumstances such spreading Would be confined to the realm of the chamfer 14 and would never extend out to the zone of the side walls of the plug 2. The advantage of this arrangement therefore is that any spreading of the peened end 12 will never operate as an obstruction to the easy withdrawal of the plug 2 from the recess 3. In practice, the plug has a snug working fit in the reeess 3, and any upsetting of the end beyond th e side walls of the plug would 0bstruet the extraction of the plug.

The fact of the detachability of the bit 4 is of no little importance in practice. The present custom in many mines is to use drills which consist of nothing more than sharpened shanks. In other words, the driller uses shanks on the order of 1 which have ends in bit-formation on the order of 4. As soon as each tool becoines dulled in use it is laid aside and another substituted.

The accumulated dulled tools will aggregate many tons of steel to be moved per day, the practice being to bundle all the dulled tools together and transport them to the surface where they are resharpened in the shop. Even in a mine of moderate proportions the amount of steel having to be thus moved Will total as much as ten to fifteen tons per` day.

By making the bits 4 detachable the maj or part of each tool will be left as placed in the mine and only the accumulated bits 4 will be gathered in a bag and sent to the surface for resharpening. Under the same condition named before the amount of steel thus handled will be reduced to approximately onehalf a ton.

Another advantage in this particular type of drilling tool is that the plug 2 of the shank 1 is readily (luplicated with equipment customarily found in a mine shop. The same forge machine by which the bits 4 are sharpened can be quickly converted into an apparatus for forming the plug 2 and lugs 5 y merely changing the dies. The advantage of this facility is that a broken shank 1 is not necessarily discarded either permanently or after its return to the factory.

From the foregoing it will be understood that the joint between the shank 1 and bit 4 comprises the outstanding feature of the invention. It is by means of its' peculiar qualities that each blow is delivered nearer to the cutting faces of the bit where it is needed, and not dissipated in portions of the bit where it will utimately work the destruction of such portions. Moreover, the blow is concentrated in the region surrounding the axial center of the tool, Whence it spreads to all portions of the Cutting faces.

It is to be observed that the bit 4 is what might be termed over-size at 15 in respect to the adjoining annular shoulder 9 of the shank 1. The top of the bit thus projects beyond the shoulder 9 and afords a clearance through which cuttings are more readily washed to the surface. The projection 15 thus acts as a baHe, tending to prevent cuttings from entering the space 11 to ultimately accumulate in the space 3 which, if permitted, would interfere with the detachment of the bit. y

As indicated in one of the foregoing brief statements of the objects of the invention, it is of importance to so regulated the tempering of the drill 4 that the Cutting edges or faces are located in the zone 16 of extreme hardness while the wings 6 (Fig. 2) of the interlocking means are located in the zone 17 of moderate hardness. Of course, there is no sharp line of demarcation between these zones, but rather a gradual increase in mildness of the temper of the metal so that the wings occur in the relatively softest part of the bit.

If the bit were of uniform hardness, that is to say, if the rim portion of the bit were as hard as the cutting faces, there would be the imminent danger of the wings 6 being broken out. But by drawng the hardness out of the rim 10 the Wings 6 are left sufliciently hard to render them tough enough to withstand the action of the lugs 5 in completing the connection.

In order to insure a non-chattering connection between the bit 4 and the plug 2 the latter is made of a diameter in excess of its length as is clearly disclosed in Figure 2. The diametrically opposite arrangement of the lugs 5 and wings 6 working in combination With the relative shortness of the plug 2 has the result of making a perfectly solid connection which will be proof against chattering in the use of the tool.

Another advantage of the foregoing proportion of the plug 2 is that the presence of the usual Wash hole 18 does not weaken the plug. This Wash hole is customarily a threeeighth ine,h bore. By providing a stocky plug there will be an ample annular rim or metallic volume around the Wash hole.

While the construction and arrangement of the improved drill is that of a generally preferred form, obvious modifications and changes may be made without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. A percussion drill comprising a bit having a recess with its floor located approximately medially of the bit, said floor having a concavity, a shank having a plug of reduced size defining a shoulder, said plug being generally longer than the recess is deep, thereby to space the shoulder from the rim of the bit when the plug is fitted in the recess, the extermity of the plug being peened to match and fit in the concavity, interlocking means including lugs on the plug and wings on the bit,

and an annular chamfer between said peen and the walls of the plug, oflsetting the bottoms of the Iugs from the floor of the recess and providing a region for the permissible extension of any offset portions of the peen.

2. A percussion drill comprising a bit having a recess, the floor of said recess having a central shallow concavity, and a shank having a plug occupying the recess, the end of the plug being peened to fit the concavity, the diameter of the plug being greater than the diameter of the concavity thereby leaving an annular overhang of the plug with reference to the floor. 4 q

3. A percussion drill comprising a bit hav- 'ing a recess, the floor of said recess having a central shallow concavity, a shank having a plug occupying the recess, the end of the plug being peened to fit the concavity, the diameter of the plug being greater than the diam- I eter of the concavity thereby leaving an annular overhang of the plug with reference to the floor, and a chamfer on the rim of the overhang providing a swaging space within the confines of the plug.

4. A percussion drill comprising a bit having a recess, the floor of said recess having a central shallow concavity, a shank having a plug occupying the recess, the end of the plug being peened to fit the concavity, the diameter of the plug being greater than the diameter of the concavit-y thereby leaving an annular overhang of the plug With reference to the floor, and a shoulder defining a point of demarcation between the plug and shank and being spaced from the rim of the bit, said bit being larger than the shoulder at the rim thus to define a projection beyond the shoulder to deflect cut-tings away from the space and prevent accumulation in the recess.

CHARLES W. DE WITT. 

